Hardener composition including 2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine

ABSTRACT

The present invention relates to 2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine, which can be used as hardener in epoxide applications.

This application is a divisional application of U.S. application Ser.No. 15/605,268 filed May 25, 2017, currently pending, which claims thebenefit of European Application No. DE 16173860.4 filed on Jun. 10,2016, the disclosure of which is expressly incorporated herein byreference.

BACKGROUND

The present invention relates to a process for producing2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine, which can beused as hardener in epoxide applications.

2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine (TMP-PDA) hasthe chemical structure depicted in formula 1.

It is known that amines may be employed as hardeners in epoxy systems.Epoxy resins are prepolymers comprising two or more epoxy groups permolecule. The reaction of these resins with a range of hardeners affordscrosslinked polymers. An overview of possible resins and hardeners,their use and properties is given in H. Schumann, “Handbuch Betonschutzdurch Beschichtung”, Expert Verlag 1992, pages 396-428.

SUMMARY

It is an object of the invention to find a process for producing2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine.

It is also an object of the invention to find a novel amine suitable forhardening epoxy systems.

DETAILED DESCRIPTION

The invention provides a process for producing2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine by

-   -   A) reacting triacetonamine (TAA) and malononitrile to afford the        intermediate        2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile,    -   and    -   B) hydrogenating        2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile in the        presence of at least one catalyst.

The production of the compound according to the invention2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine proceeds instep A) via a Knoevenagel condensation between triacetonamine (TAA) andmalononitrile. The reaction may be performed in a solvent or in asolvent-free reaction system under mild reaction conditions, preferablyat 20-40° C. and atmospheric pressure. The catalyst employed ispreferably zirconyl chloride or piperidine. After complete conversion ofthe reactants the intermediate2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile (cf. structureformula 2 in Example 1) may be precipitated out as solid by cooling thereaction solution. A further purification may be effected bydistillation for example.

The production of TMP-PDA from2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile is effected instep B) by hydrogenation which may be performed in one or more stages.When a plurality of hydrogenation reactions are used the individualstages may be performed in a reactor having different catalyst zones orin a plurality of separate or serially connected reactors. Thehydrogenation is preferably effected in fixed-bed reactors. Suitablereactor types are, for example, shaft furnaces, tray reactors or shelland tube reactors. It is also possible to connect a plurality offixed-bed reactors in series for the hydrogenation, each of the reactorsbeing operated in downflow mode or in upflow mode as desired.

The catalysts employed may in principle be any catalysts which catalyzethe hydrogenation of nitrile groups with hydrogen. Particularly suitablecatalysts are nickel, copper, iron, palladium, rhodium, ruthenium andcobalt catalysts, very particularly palladium, ruthenium and cobaltcatalysts. To increase activity, selectivity and/or service life, thecatalysts may comprise additional doping metals or other modifiers.Typical doping metals are, for example, Mo, Fe, Ag, Cr, Ni, V, Ga, In,Bi, Ti, Zr and Mn, and the rare earths. Typical modifiers are, forexample, those with which the acid-base properties of the catalysts canbe influenced, preferably alkali metals and alkaline earth metals orcompounds thereof, preferably magnesium and calcium compounds, and alsophosphoric acid or sulphuric acid and compounds thereof.

The catalysts may be employed in the form of powders or shaped bodies,for example extrudates or compressed powders. It is possible to employunsupported catalysts, Raney-type catalysts or supported catalysts.Preference is given to Raney-type and supported catalysts. Suitablesupport materials are, for example, silicon dioxide, aluminium oxide,aluminosilicates, titanium dioxide, zirconium dioxide, kieselguhr,aluminium-silicon mixed oxides, magnesium oxide and activated carbon.The active metal can be applied to the support material in a mannerknown to those skilled in the art, for example by impregnation, sprayapplication or precipitation. Depending on the method of catalystproduction, further preparation steps known to those skilled in the artare necessary, for example drying, calcining, shaping and activation.Further assistants, for example graphite or magnesium stearate, mayoptionally be added for shaping. The required volume of thehydrogenation catalysts to be used is determined by the LHSV value(liquid hourly space velocity) which is dependent on operating pressure,temperature, concentration and catalyst activity and must be adhered toin order to ensure as complete a hydrogenation as possible.

Production of the inventive diamine TMP-PDA preferably employshydrogenation catalysts based on palladium and/or cobalt. Thesecatalysts show particularly good activity to achieve a high yield.

The catalysts may be employed in the form of powders or fixed-bedcatalysts. The hydrogenation may be effected in batch mode or incontinuously operated plants.

The reaction conditions for the hydrogenation are between 20-120° C. and20-300 bar.

The hydrogenation may be performed in one or more stages. Thehydrogenation is preferably performed in two stages. In the first ofthese stages, reaction conditions of 20-120° C. and 20-300 bar,preferably 40-100° C. and 25-150 bar and particularly preferably 60-90°C. and 40-80 bar are chosen. In the second stage of the hydrogenation,reaction conditions of 20-120° C. and 20-300 bar, preferably 50-115° C.and 50-200 bar and particularly preferably 80-110° C. and 80-140 bar arechosen.

The first stage of the hydrogenation preferably employs a palladiumcatalyst.

The second stage of the hydrogenation preferably employs a Raney-typecatalyst. It is particularly preferable when after activation thecatalyst in its entirety has the following composition in weight percent(wt %), the proportions summing to 100 wt % based on the metals present:

cobalt: 57 to 84 wt %

aluminium: 10 to 40 wt %

chromium: 1 to 2 wt %

nickel: 2 to 4 wt %

and

with particle sizes of the catalyst, i.e. of the pellet particles,having a statistical distribution between 3 to 7 millimeters (mm),wherein up to 10 percent of the particles may also be outside the statedrange of the stated lower limit or upper limit but also in each case upto 10 percent may be outside the stated range of the stated lower limitand upper limit.

The reaction mixture leaving the hydrogenation is further purified bycustomary methods to obtain TMP-PDA of the desired quality. Any standardseparation methods, for example distillation, flash evaporation,crystallization, extraction, sorption, permeation, phase separation orcombinations of the above, may be employed here. The purification may beconducted continuously, batchwise, in one or more stages, under vacuumor under pressure. The purification of TMP-PDA is preferably performedby distillation, for example.

The purification is preferably achieved by distillation under pressureand/or under vacuum in a plurality of steps. Any desired distillationcolumns with or without internals may be used to this end, for exampledephlegmators, dividing walls, unordered internals or random packings,ordered internals or structured packings, or trays with or withoutforced flow.

Use as Epoxy Hardener:

The invention also provides for the use of2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine (TMP-PDA) as ahardener in epoxy resin compositions.

Contemplated as the epoxy resin component are in principle all epoxyresins that may be cured with amines. Epoxy resins include, for example,polyepoxides based on bisphenol A diglycidyl ether, bisphenol Fdiglycidyl ether or cycloaliphatic types. However, preference is givento using epoxy resins based on bisphenol A and optionally those based onbisphenol F, optionally also in admixture. The resins and hardeners arepreferably employed in equivalent amounts. However, deviations from thestoichiometric ratio are also possible.

EXAMPLES Example 1: Production of2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine, TMP-PDA StepA): Synthesis of 2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile

-   -   A 1 L three-necked flask fitted with two dropping funnels was        initially charged with 384.5 g of triacetonamine (TAA) in 350 g        of dioxane. The reactor contents were kept at room temperature.    -   148.5 g of malononitrile were diluted with 150 g of dioxane and        initially charged into a dropping funnel.    -   1.5 g of zirconyl chloride (catalyst) were dissolved in 30 g of        deionized water and filled into the second dropping funnel.    -   The contents of both dropping funnels were then simultaneously        added dropwise to the reactor and the reactor was then stirred        for one hour at room temperature (between 20-30° C.).    -   The reaction mixture formed was cooled with an ice bath and the        thus precipitated product        2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile was        filtered off.    -   The further purification was effected by recrystallization in a        solvent mixture of 50 wt % of cold ethanol and 50 wt % of cold        deionized water and subsequent filtration and drying in a vacuum        drying cabinet (45° C., 10 mbar, 3 h).    -   The product composition was determined by gas chromatography.

The yield of 2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile was90%.

Step B1): Partial Hydrogenation of2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile to ProduceTMP-PDA, 1st Hydrogenation Stage

-   -   150 ml of the fixed-bed catalyst Pd/aluminium oxide (1 wt % Pd)        was installed in a 2 L pressure autoclave fitted with a catalyst        cage.    -   1 L of solution comprising 10 wt % of        2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile (product        from step A) in tetrahydrofuran was initially charged for the        reaction.    -   The reaction was effected at 75° C. with 50 bar of hydrogen for        5 h.    -   The entire product solution was discharged from the reactor.    -   The composition of the product solution was determined by gas        chromatography.

Step B2, 2nd Hydrogenation Stage): Full Hydrogenation of ProductSolution from Step B1

150 ml of activated Raney cobalt alloy pellets were installed as a fixedbed in a 2 L pressure autoclave fitted with a catalyst cage. Thiscatalyst had the following composition in weight percent (wt %), theproportions summing to 100 wt % based on the metals present:

cobalt: 75.9 wt %

aluminium: 20.0 wt %

chromium: 1.5 wt %

nickel: 2.6 wt %

A sieve fraction of the catalyst having a statistical distributionbetween 2.0 and 5.0 millimeters (mm) was employed, wherein up to 10% ofthe particles may be above the stated upper limit and up to 10% of theparticles may be below the stated lower limit.

-   -   1 L of reaction solution (partially hydrogenated product from        step B1 in THF) was initially charged for the reaction.    -   The reaction was effected at 100° C. with 100 bar of hydrogen        for 5 h.    -   The composition of the product solution was determined by gas        chromatography.    -   For use of TMP-PDA as a hardener in epoxy resin systems the        product obtained was purified by distillation.

The yield of the two-stage hydrogenation was 85 wt % of TMP-PDA based onthe employed substance2-(2,2,6,6-tetramethylpiperidin-4-ylidene)malononitrile from step A.

Example 2: TMP-PDA as a Hardener in Epoxy Resin Systems

The epoxy resin employed was the standard resin Epikote 828 from Hexionhaving an epoxy equivalent weight of 188 g/eq. Said resin was blended instoichiometric equality of the H equivalents with the hardener componentTMP-PDA (cf. Table 1) and the glass transition temperature (Tg) wasdetermined after a dwell time of one hour at a defined curingtemperature (Table 2). The respective reaction conversions weredetermined via the recorded evolution of heat from the curing reactionin relation to the maximum evolution of heat (Table 3).

TABLE 1 Ratio of resin to hardener Hardener component 100 TMP-PDA (g)Amount of epoxy resin 441 (g) per 100 g of hardener

TABLE 2 Glass transition temperatures (Tg) after one hour of curing atvarious temperatures Tgmax. (DSC ) 175° C. Tg after 1 h 50° C.  37° C.Tg after 1 h 70° C.  76° C. Tg after 1 h 90° C. 102° C. Tg after 1 h110° C. 128° C. Tg after 1 h 130° C. 150° C. Tg after 1 h 150° C. 162°C.

TABLE 3 Conversions Conversion after 1 h 50° C.  62% Conversion after 1h 70° C.  80% Conversion after 1 h 90° C.  90% Conversion after 1 h 110°C.  95% Conversion after 1 h 130° C.  97% Conversion after 1 h 150° C.100%

As is readily apparent to a person skilled in the art from Table 1,Table 2 and Table 3, TMP-PDA is a suitable hardener component in epoxyresin systems.

The invention claimed is:
 1. A hardener in epoxy resin composition, thehardener comprising2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine of formula 1


2. The hardener of claim 1 wherein the epoxy resin composition is aprepolymer comprising two or more epoxy groups per molecule.
 3. Thehardener of claim 1 wherein the epoxy resin composition is selected fromthe group consisting of polyepoxides based on bisphenol A diglycidylether, polyepoxides based on bisphenol F diglycidyl ether, andcycloaliphatic epoxy resin.
 4. The hardener of claim 1 wherein the epoxyresin composition comprises bisphenol A diglycidyl ether.
 5. Thehardener of claim 1 wherein the epoxy resin composition comprisesbisphenol F diglycidyl ether.
 6. A composition comprising a) a hardenercomprising 2-(2,2,6,6-tetramethylpiperidin-4-yl)propane-1,3-diamine offormula 1

and b) an epoxy resin composition.
 7. The composition of claim 6 whereinthe epoxy resin composition is a prepolymer comprising two or more epoxygroups per molecule.
 8. The composition of claim 6 wherein the epoxyresin composition is selected from the group consisting of polyepoxidesbased on bisphenol A diglycidyl ether, polyepoxides based on bisphenol Fdiglycidyl ether, and cycloaliphatic epoxy resin.
 9. The composition ofclaim 6 wherein the epoxy resin composition comprises bisphenol Adiglycidyl ether.
 10. The composition of claim 6 wherein the epoxy resincomposition comprises bisphenol F diglycidyl ether.
 11. The compositionof claim 6 wherein the epoxy resin comprises a mixture of bisphenol Adiglycidyl ether and bisphenol F diglycidyl ether.